Pre-85 125s:
The 81-84 RMs are all good if you can handle the peaky motors.
84 CR is probably the best choice once you fix the shock and fit one of Russell's alloy clutch covers.
84 KX is good if you find one with a decent frame.
The 84 KTM125 has tons of potential, but usual old KTM ownership hassles apply (parts prices, mostly).
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Pre-90 125s:
87+ CR is a safe bet. 87 is arguably the best of them. The 86 model isn't bad either, but the non-cartridge forks and rear drum isn't cool when the later bikes have them.
88 KX is great. Almost an enduro bike spread of power, makes them easier to ride than any other bike in the class. Still makes more power than the YZ or RM... 89 model went backwards with flat power and less-good forks. Power valves are a PITA.
89 RM would probably be the pick of them, but they're too peaky and typical 80s/90s Suzuki build quality... Also PV dramas.
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Pre-85 250s:
YZ or CR are the bikes to own. I'd get the CR for the relatively modern ergos and great front brake.
The YZ is better suited to shorter riders.
KX too rare, too hard to get bits for, too likely to have a broken frame.
RM too peaky.
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Pre-90 250s:
87 CR is my pick, but the rare 88 RM is supposed to be excellent. I'd probably chase a US-import 89 KX250 if I wanted a serious race bike for this class.
88 KX would be great, except it has a big midrange wallop that makes it hard to ride. 89 KX250s have a better motor, but crappy forks. In fact, all of the 89 models were universally handicapped by shitty early USD forks that were clearly inferior to their earlier models' RWU forks.
89 RM250 is a lovely modern feeling bike, but has a big midrange hit and PV dramas.
The 250 Yammies were generally off the pace by the late 80s. The 88 is the high point (decent forks!).
